1. Field of the Invention
This invention is directed toward novel alpha olefin copolymers having a narrow molecular weight distribution (MWD) and a broad compositional distribution (CD), and a process for making ame.
2. Description of Related Art
Ethylene-propylene copolymers, particularly elastomers, are important commercial products. Two basic types of elastomeric ethylene-propylene copolymers are commercially available. Ethylene-propylene copolymers (EPM) are saturated compounds requiring vulcanization with free radical generators such as organic peroxides. Ethylene-propylene terpolymers (EPDM) contain a small amount of non-conjugated diolefin , such as dicyclopentadiene, 1,4-hexadiene or ethylidene norbornene, which provides sufficient unsaturation to permit vulcanization with sulfur. Such polymers that include at least two monomers, i.e. EPM and EPDM, will hereinafter be collectively referred to as copolymers.
These elastomeric copolymers have outstanding resistance to weathering, good heat aging properties and the ability to be compounded with large quantities of fillers and plasticizers resulting in low cost compounds which are particularly useful in automotive and industrial mechanical goods applications. Typical automotive uses are tire sidewalls, inner tubes, radiator and heater hose, vacuum tubing, weather stripping and sponge doorseals and Viscosity Index (V.I.) improvers for lubricating oil compositions. Typical mechanical goods uses are for appliance, industrial and garden hoses, both molded and extruded sponge parts, gaskets and seals and conveyor belt covers. These copolymers also find use in adhesives, appliance parts as in hoses and gaskets, wires and cable and plastics blending.
As can be seen from the above, based on their respective properties, elastomeric EPM and EPDM copolymers find many and varied uses. It is known that the properties of such copolymers which make them useful in a particular application are, in turn, determined by their composition and structure. For example, the ultimate properties of an EPM or EPDM copolymer are determined by such factors as composition, compositional distribution, sequence distribution, molecular weight, and molecular weight distribution (MWD).
The efficiency of peroxide curing depends on composition. As the ethylene level increases, it can be shown that the "chemical" cross-links per peroxide molecule increase. Ethylene content also influences the rheological and processing properties, because crystallinity can be introduced. The crystallinity present at very high ethylene contents may hinder processibility and may make the cured product too "hard" at temperatures below the crystalline melting point to be useful as a rubber.
The properties of EPM and EPDM copolymers are a function of the catalyst system and polymerization process used to produce them. Elastomeric olefin copolymers may be produced at relatively low polymerization temperatures and pressures by means of the so called Ziegler catalysts which comprise a transition metal compound used in combination with a metal alkyl. More specifically, catalyst systems based on a combination of a vanadium compound, an aluminum alkyl or aluminum alkyl halide and, in some cases, a halogen-containing organic compound which serves as a polymerization promoter are known in the art.
For example, U.S. Pat. No. 4,540,753 relates to ethylene copolymers with narrow molecular weight distribution (MWD) and a narrow intermolecular composition distribution (Inter-CD). The catalyst system used in this reference comprises a hydrocarbon-soluble vanadium compound having the formula: ##STR1## and an organo-aluminum compound. In the polymerization process, the catalyst components are premixed in the premixing device and aged for 1-50 seconds. The inlet temperature of the reaction mixture is about -50.degree. to 150.degree. C.
As pointed out in the above mentioned U.S. Pat. No. 4,540,753, Inter-CD defines the compositional variation, in terms of ethylene content, among polymer chains. It is expressed as the minimum deviation (analogous to a standard deviation) in terms of weight percent ethylene from the average ethylene composition for a given copolymer sample needed to include a given weight percent of the total copolymer sample which is obtained by excluding equal weight fractions from both ends of the distribution. The deviation need not be symmetrical. When expressed as a single number for example 15% Inter-CD, it shall mean the larger of the positive or negative deviations. For example, for a Gaussian compositional distribution, 95.5% of the polymer is within 20 wt.% ethylene of the mean if the standard deviation is 10%. The Inter-CD for 95.5 wt.% of the polymer is 20 wt.% ethylene for such a sample.
G.B. Patent 902,385 teaches a process of preparing a copolymer of ethylene and higher 1-olefin that is essentially homogeneous as to its composition using a catalyst system based on VOY.sub.n and AlR.sub.3 where Y is alkoxide or acetyacetonate group, and n is 2 or 3, and R is a hydrocarbon radical. A mixture of carbon tetrachloride and an inert organic liquid solvent or carbon tetrachloride alone is used as the solvent for the copolymerization reaction. Temperature is within the range of from 0.degree. C. to 125.degree. C., more preferably from 25.degree. C. to 80.degree. C. A molar ratio of Al/V is from 3 to 8.
U.S. Pat. No. 3,000,866 teaches ethylene copolymers with about 20% ethylene units by weight and at least 25% alpha-olefin units by weight and about 0.5% to 10% of dicyclopentadiene units by weight. The catalyst system used in this disclosure is made by mixing vanadium tetrachloride or vanadium oxytrichloride with (R).sub.3 Al or (R).sub.2 AlX. The polymerization is conducted by contacting ethylene and dicyclopentadiene in a solution of tetrachloro ethylene with the said catalyst system at temperatures between about 20.degree. C. to 100.degree. C.
GB Patent 1,005,282 relates to a catalyst system such as vanadium or chromium acylacetonate, vanadyl diacylacetonate, and vanadyl alkyl orthovanadate and a halogen-free metal organic compound such as aluminum trialkyl or aluminum alkenyl for the preparation of linear head-to-tail high molecular weight homopolymers of alpha-olefin having the general formula R--CH.dbd.CH.sub.2. The polymerization is carried out in the presence of a halogenated hydrocarbon compound such as chloroform, methylene chloride or a mixture thereof. The polymerization is carried out at temperatures of from -80.degree. C. to +125.degree. C.
U.S. Pat. No. 3,301,834 relates to a process for the polymerization of ethylene and for the copolymerization of ethylene with other ethylenically unsaturated hydrocarbons. The catalyst system comprising vanadium compounds (VOCl.sub.3 or VCl.sub.4) and organoaluminum compounds is formed in the presence of a halogenated compound such as benzotrichloride. The ratio of halogenated compound to vanadium compound is preferably from 10:1 to 100:1. The molar ratio of V/Al generally is 1:3 to 1:30, but higher ratios up to 1:3000 are disclosed to be operable. The polymerization temperature range is from room temperature to about 150.degree. C.
U.S. Pat. No. 3,349,064 also relates the same catalyst system as that defined in U.S. Pat. No. 3,301,834 except that the halogenated promoter is a group of unsaturated carboxylic compounds containing at least 4 halogen atoms, at least 2 of which are attached to doubly bonded carbon atoms and at least 1 of which is attached to a singly bonded carbon atom alpha to the double bond (e.g., 2, 2, 3, 4, 5, 5-hexachlorocyclopentene). The use of VCl.sub.4, TEA and hexachlorocylocpentadiene is described in example 6. The molar ratio of promoter to vanadium compound is preferably from 10:1 to 100:1. The molar ratio of V/Al is 1:3 to 1:30; 1:60 is disclosed to be operable.
U.S. Pat. No. 3,489,729 relates to a method of making EPDM polymer by using the catalyst system comprising R.sub.3 Al organo-aluminum compounds and vanadium compounds having formula VOY.sub.n, together with halogen-containing compounds such as hydrogen chloride, elemental chlorine, benzyl chloride, or t-butyl chloride. The temperature for the polymerization is -100.degree. to 200.degree. F. The molar ratio of organoaluminum compound to vanadium compound is in the range of 3/1 to 20/1. The amount of active halogen-containing compound based on vanadium compound is 1 to 30 mols per mol of vanadium compound.
BE Patent 592,247 teaches a process for preparing copolymer of ethylene with alpha-olefins whose molecular weight depends on the amount of halogenated alkanes used. Triisobutyl aluminum ([(CH.sub.3).sub.2 CH.sub.2 ].sub.3 Al), vanadium tetrachloride (VCl.sub.4) and carbon tetrachloride (CCl.sub.4) may be used as a catalyst system.
GB Patent 1,059,865 relates to the polymerization of ethylene, or ethylene together with one or more olefin monomers. TEA, CCl.sub.4, CHCl.sub.3, and vanadium di-isopropyl salicylate are used as the catalyst system.
The breadth of the intermolecular compositional distribution (CD) and molecular weight distribution (MWD) of polymers such as prepared by the above referenced disclosures are largely a function of the particular catalyst system employed to prepare the polymer. Such catalyst systems generally yield polymer with either narrow CD and narrow MWD or broad CD and broad MWD. Until the present invention, ethylene copolymers (EPM or EPDM) having a broad CD and at the same time a narrow MWD are not believed to have been disclosed in the art. Such elastomers are especially useful in that they possess novel combinations of properties such as excellent green strength and processability which leads to superior performance in a number of applications.